Concrete admixture

ABSTRACT

A concrete admixture is provided, which is effective in imparting fluidity to a hydraulic composition such as cement paste, mortar or concrete, particularly in maintaining the fluidity of the composition and which hardly retards the hardening property of the composition. The concrete admixture comprises a copolymer comprising, as structural units, units derived from an ethylenically unsaturated monomer (a) having 25 to 300 moles of C 2  -C 3  oxyalkylene groups per mole of copolymer and units derived from a monomer (b) of an alkyl, alkenyl or hydroxyalkyl ester of an ethylenically unsaturated mono- or di-carboxylic acid.

This application is the national phase under 35 U.S.C. §371 of prior PCTInternational Application No., PCT/JP97/02095, which has anInternational filing date of Jun. 18, 1997, which designated the UnitedStates of America, the entire contents of which are hereby incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to a concrete admixture. Morespecifically, it relates to a concrete admixture which is extremelyeffective in imparting fluidity to a hydraulic composition such ascement paste, mortar and concrete, particularly in retention of fluidityof the composition, and which hardly retards the hardening property ofthe composition.

BACKGROUND OF THE INVENTION

So-called high performance water reducing agents have been known for usein concrete admixtures and can impart high fluidity. Examples thereofinclude salts of naphthalenesulfonic acid/formaldehyde condensates(naphthalene derivatives), salts of melaminesulfonic acid/formaldehydecondensates (melamine derivatives), salts of sulfanilic acid/phenolformaldehyde co-condensates (aminosulfonic acid derivatives), salts ofpolycarboxylic acids (polycarboxylic acid derivatives) and so on.

Each of these admixtures has some problems even though each hasexcellent functions. For example, the naphthalene derivatives and themelamine derivatives are excellent in hardening characteristics,however, are problematic with regard to retention of fluidity (owing totheir tendency to cause a slump loss). On the other hand thepolycarboxylic acid derivatives is disadvantaged due to its retardingeffect on the hardening property of the composition. Recentlypolycarboxylic acid concrete admixtures which can impart excellentfluidity have been developed, which makes it possible to attainexcellent dispersion with a reduced amount of an admixture, and therebythe problem of retarding the hardening property is being solved. Suchadmixtures include water-soluble vinyl copolymers such as copolymers ofpolyalkylene glycol monoester monomers having unsaturated bonds withacrylic acid and/or unsaturated dicarboxylic acid monomers (see JP-A58-74552, JP-A 62-78137, JP-A 62-119147, JP-A 3-75252 and JP-A59-162160).

These water-soluble copolymers each exhibit an excellent dispersingeffect even at relatively low concentrations, so that the retardation isimproved comparatively. Further, as described in JP-A 59-162160, theyare somewhat effective in maintaining the dispersion. However, thecopolymers cannot satisfactorily effect on retention of fluidity for along time.

Under these circumstances, the inventors of the present invention haveproposed in JP-A 7-223852 (corresponding to WO-A 95/16643) animprovement of slump loss by the use of a copolymer having a longpolyoxyalkylene chain as an admixture. The technique described thereinmakes it possible to maintain the slump at a suitable level for a longperiod of time for example 60 to 90 minutes.

However, ideally the slump is maintained for about 2 hours to cope withinevitable delays in concrete processing due to traffic jams or troublesin construction. Therefore, the above effect of maintaining the slumpfor about 90 minutes is still insufficient and ideally would be furtherimproved. Further, an improvement in the effect of maintaining the slumpis liable to cause a problem of retarding the hardening property, sothat such an improvement is also required to be attained withoutretarding the hardening property.

SUMMARY OF THE INVENTION

The inventors of the present invention have intensively studied ongradual supply of a dispersing agent as a means for maintaining thedispersed state of cement particles and thereby keeping the slump for along time. Namely, the inventors of the present invention have designedthe molecular structure of a dispersing agent from the viewpoint of therate of adsorption in a strongly ionized concrete system, and have foundthat a vinyl copolymer comprising an oxyalkylene group and a specificmonomer exhibits an extremely excellent slump-maintaining effect andthat the copolymer makes it possible to maintain the slump for a timemuch longer than that of the prior arts without retarding the hardeningproperty. The present invention has been accomplished on the basis ofthese findings.

Namely, the present invention provides a concrete admixture comprising acopolymer comprising, as structural units, units derived from anethylenically unsaturated monomer (a) having 25 to 300 moles of C₂ -C₃oxyalkylene groups and units derived from a monomer (b) of an alkyl,alkenyl or hydroxyalkyl ester of an ethylenically unsaturated mono- ordi-carboxylic acid.

The present invention provides a method for dispersing a cement mixturewith the copolymer.

The present invention provides a concrete composition comprising cement,aggregates and the copolymer.

The present invention provides use of the copolymer to mix and dispersea cement mixture.

The present invention also provides an embodiment, in which thecopolymer comprising 10 to 30 mole % of the units (a), 50 to 70 mole %of the units (b) and 10 to 30 mole % of the units (c).

According to the invention, the dispersion can be maintained over aperiod of 120 minutes or longer. Retardation of the hardening propertycan be thereby reduced.

When the concrete admixture of the present invention is used forconcrete, an extremely excellent slump-maintaining effect can beattained. Although the present invention should not be construed to bebound by the following theory, the reason for which is considered to bethat the dispersing agent is gradually taken into hydrates of cement toprevent the fluidity from lowering. In other words, it is assumed thatoxyalkylene groups and the units derived from the specific monomer inthe copolymers of the present invention may influence the rate ofadsorption to cement.

The concrete admixture of the present invention comprises a copolymercomprising, as structural units, units derived from an ethylenicallyunsaturated monomer (a) having 25 to 300 moles of C₂ -C₃ oxyalkylenegroups and units derived from a monomer (b) of an alkyl, alkenyl orhydroxyalkyl ester of an ethylenically unsaturated mono- ordi-carboxylic acid. Therefore, carboxyl groups which serves as anadsorbing group is gradually increased through hydrolysis of ester withan alkali to result in supplying a freshly formed dispersant, which maybe the reason why the fluidity is not lowered but maintained for a longperiod of time. When the copolymer has lengthened side chains by anincrease in the mole number of oxyalkylene groups added, it exhibits anenhanced dispersing effect due to steric repulsion and therefore canimpart fluidity even when a reduced amount is used. Therefore, thesurface hydration of cement is little hindered to result in a slightretardation of the hardening property. However, the present invention isnot limited by these assumptions.

DETAILED DESCRIPTION

In the copolymer of the present invention, the ethylenically unsaturatedmonomer (a) having 25 to 300 moles of C₂ -C₃ oxyalkylene groups includes(meth)acrylic esters of methoxypolyalkylene glycols; polyalkylene glycolmonoallyl ethers; and adducts of dicarboxylic acids such as maleicanhydride, itaconic anhydride, citraconic anhydride, maleic acid,itaconic acid and citraconic acid, acrylamide and acrylalkylamide withC₂ -C₃ oxyalkylene groups. Preferable examples of the monomer (a)include those represented by the following general formula (A): ##STR1##

wherein R₁ and R₂ are each hydrogen atom or methyl, AO is a C₂ -C₃oxyalkylene group, n is a number of 25 to 300 and X is hydrogen atom ora C₁ -C₃ alkyl group.

Specific examples of the monomer (a) represented by the above formula(A) include acrylic and methacrylic esters of polyalkylene glycolsblocked with an alkyl group at one end such as methoxypolyethyleneglycol, methoxypolyethylenepolypropylene glycol, ethoxypolyethyleneglycol, ethoxypolyethylenepolypropylene glycol, propoxypolyethyleneglycol and propoxypolyethylenepolypropylene glycol; and adducts ofacrylic and methacrylic acids with ethylene oxide and propylene oxide.The molar addition number of the oxyalkylene group is 25 to 300. Whenboth ethylene oxide and propylene oxide are used, the copolymer may takeany form of random addition, block addition and alternating addition. Itis preferable from the viewpoint of not causing any retardation of thehardening of concrete that the number of the oxyalkylene group is 50 orabove, particularly 110 or above. When the number exceeds 300, not onlythe polymerizability of the monomer will be poor but also the resultingcopolymer will be poor in the dispersing effect.

Preferable examples of alkyl, alkenyl or hydroxyalkyl ester of anethylenically unsaturated mono- or di-carboxylic acid to be used as themonomer (b) in the present invention include unsaturated monocarboxylateester represented by, e.g., the following general formula (B): ##STR2##

wherein R₃ is hydrogen atom or methyl and R₄ is a C₁ -C₁₈ alkyl oralkenyl group or a C₂ -C₆ hydroxyalkyl group.

Specific examples of the monomer (b) include C₁ -C₁₈ linear and branchedalkyl (meth)acrylates; C₁ -C₁₈ linear and branched alkenyl(meth)acrylates; C₂ -C₆ hydroxyalkyl (meth)acrylates; di(C₁ -C₁₈ linearand branched alkyl) esters of maleic acid, fumaric acid, itaconic acidand citraconic acid; and di(C₁ -C₁₈ linear and branched alkenyl) estersof maleic acid, fumaric acid, itaconic acid and citraconic acid. It isparticularly preferable in the solubility of the copolymer in water thatR₄ in the above general formula (B) be one having 1 to 4 carbon atoms,though R₄ is not particularly limited in the form but may be any oflinear and branched ones.

The copolymer according to the present invention is excellent in theeffect of maintaining the slump, preferably when the proportions of theunits (a) and (b) are 0.1 to 50 mole % and 50 to 99.9 mole %respectively. In particular, when the proportions of the monomers (a)and (b) are 1 to 40 mole % and 60 to 99 mole % respectively, theresulting copolymer exhibits an excellent effect of low fluidity lossand is extremely excellent in the retention of slump. When theproportions of the monomers are outside the above ranges, the copolymershows poor retention of slump.

The copolymer according to the present invention may further containunits derived from a monomer (c) as structural units. The monomer (c) isan ethylenically unsaturated monocarboxylic acid or a salt thereof, oran ethylenically unsaturated dicarboxylic acid or an anhydride or saltthereof, and can be represented by, e.g., the following general formula(C): ##STR3##

wherein M₁ is hydrogen atom, an alkali metal, an alkaline earth metal,ammonium, an alkylammonium or a substituted alkylammonium group; R₅, R₆and R₇ are each hydrogen atom, methyl or (CH₂)_(m2) COOM₂ ; M₂ has thesame definition as M₁ ; m₂ is 0 or 1.

Specific examples of the monomer (c) to be used include monocarboxylicacid monomers such as acrylic acid, methacrylic acid and crotonic acidand salts thereof with alkali metals, ammonium, amines and substitutedamines; and unsaturated dicarboxylic acid monomers such as maleic acid,itaconic acid, citraconic acid and fumaric acid and salts thereof withalkali metals, alkaline earth metals, ammonium, amines and substitutedamines. Further, the copolymer may contain other monomer such asacrylamide, vinyl acetate, styrene and vinyl chloride.

In the case wherein the copolymer contains the monomer unit (c), thecopolymer is excellent in the effect of maintaining the slump,preferably when the proportions of the units (a), (b) and (c) are 0.1 to50 mole %, 50 to 90 mole % and 0.1 to 50 mole % respectively. Inparticular, when the proportions of the units (a), (b) and (c) are 5 to40 mole %, 50 to 90 mole % and 5 to 40 mole %, the resulting copolymerexhibits almost no fluidity loss and shows excellent balance betweeninitial dispersibility and retention of fluidity to permit a reductionin the amount of the admixture used.

The copolymer according to the present invention can be prepared byknown processes, e.g. solution polymerization described in JP-A62-119147 and JP-A 62-78137. That is, the copolymer can be prepared bypolymerising the monomers (a) and (b), or the monomers (a), (b) and (c)in a suitable solvent at the above-described reacting ratio.

The solvent to be used in the solution polymerization includes water,methyl alcohol, ethyl alcohol, isopropyl alcohol, benzene, toluene,xylene, cyclohexane, n-hexane, ethyl acetate, acetone, methyl ethylketone and so on. It is preferable from the viewpoints of handleabilityand reaction equipment to use water, methyl alcohol, ethyl alcohol andisopropyl alcohol.

Examples of the polymerization initiator usable in an aqueous mediuminclude ammonium and alkali metal salts of persulfuric acid; hydrogenperoxide; and water-soluble azo compounds such as2,2'-azobis(2-amidinopropane) dihydrochloride and2,2'-azobis(2-methylpropionamide) dehydrate. Examples of thepolymerization initiator usable in conducting the solutionpolymerization in a non-aqueous medium include peroxides such as benzoylperoxide and lauroyl peroxide; and aliphatic azo compounds such asazobisisobutyronitrile.

A polymerization accelerator such as sodium hydrogensulfite and aminecompounds may be used simultaneously with the polymerization initiator.Further, a chain transfer agent such as 2-mercaptoethanol,mercaptoacetic acid, 1-mercaptoglycerin, mercaptosuccinic acid oralkylmercaptan may be simultaneously used for the purpose of controllingthe molecular weight.

It is preferable that the copolymer according to the present inventionhave a weight-average molecular weight of 8,000 to 1,000,000, stillpreferably 10,000 to 300,000 (in terms of polyethylene glycol asdetermined by gel permeation chromatography). When the molecular weightis too large, the copolymer will be poor in the dispersing property,while when it is too small, the copolymer will be poor in the propertyof maintaining the slump.

The copolymer according to the present invention may further comprisesother comonomers, as far as the effects of the present invention are notadversely affected. Examples of such comonomers include acrylonitrile,methallylsulfonic acid, acrylamide, methacrylamide, styrene andstyrenesulfonic acid.

It is preferable that the amount of the concrete admixture added toconcrete be 0.02 to 1.0% by weight, still preferably 0.05 to 0.5% byweight based on cement in terms of solid matter.

The concrete admixture of the present invention may further contain theabove-described high performance water reducing agent.

Examples of the high performance water reducing agent includenaphthalene derivatives such as Mighty 150 (a product of KaoCorporation), melamine derivatives such as Mighty 150V-2 (a product ofKao Corporation), amino-sulfonic acid derivatives such as Paric FP (aproduct of Fujisawa Chemicals), and polycarboxylic acid derivatives suchas Mighty 2000WHZ (a product of Kao Corporation). Among these known highperformance water reducing agents, it is particularly preferable to usea copolymer described in JP-A 7-223852 (corresponding to WO-A 95/16643)which is prepared by copolymerizing a polyalkylene glycol monoestermonomer, wherein the polyalkylene glycol moiety is composed of 110 to300 moles of oxyalkylene groups having 2 to 3 carbon atoms, with anacrylic acid monomer, because the copolymer is excellent in maintainingthe fluidity showing little retardation of the hardening property.

It is preferable from the viewpoint of maintaining the fluidity that theweight ratio of the concrete admixture of the present invention to thehigh performance water reducing agent lies between 1:99 and 99:1 (withthe proviso that the sum total is 100% by weight), more preferablybetween 10:90 and 90:10.

The concrete admixture of the present invention may be used incombination with other known additives. Examples of such additivesinclude an air entraining (AE) agent, an AE water-reducing agent, aplasticizer, a retarder, an early-strength enhancer, an accelerator, afoaming agent, a blowing agent, an antifoaming agent, a thickener, awaterproofing agent, a defoaming agent, quartz sand, blast furnace slag,fly ash, silica fume and so on.

The concrete admixture of the present invention can be added to acomposition containing a hydraulic cement. Examples of the compositioninclude cement pastes, mortars and concretes, though the composition isnot particularly limited.

EXAMPLES

The present invention will now be described specifically by referring tothe following Examples, though the present invention is not limited bythem. In the Examples, all percentages are by weight.

The weight-average molecular weights of copolymers given in the Examplesare those in terms of polyethylene glycol as determined by gelpermeation chromatography.

The compounds used in the following Examples as the monomer (a) will nowbe listed together with their symbols, wherein EO and PO refer toethylene oxide and propylene oxide respectively; and molar additionnumbers are given in terms of average ones.

A-1: methoxypolyethylene glycol methacrylate (The number of EO added:130)

A-2: methoxypolyethylene glycol methacrylate (The number of EO added:185)

A-3: methoxypolyethylene glycol acrylate (The number of EO added: 280)

A-4: methoxypolypropylenepolyethylene glycol(random adduct) methacrylate(The number of EO added: 125, number of PO added: 15)

A-5: adduct of maleic acid with EO (The number of EO added: 120)

A-6: adduct of allyl alcohol with EO (The number of EO added: 120)

A-7: adduct of acrylamide with EO (The number of EO added: 118)

A-8: methoxypolyethylene glycol methacrylate (The number of EO added:28)

A-9: methoxypolyethylene glycol methacrylate (The number of EO added:90)

A-10 (Comp.): methoxypolyethylene glycol methacrylate (The number of EOadded: 350)

A-11 (Comp.): methoxypolyethylene glycol methacrylate (The number of EOadded: 13)

Production Examples for the copolymers will now be described.

Production Example 1 (Admixture C-1)

Water (26 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.05 mol of monomer A-1 and 0.95 mol of methyl acrylate, a 20% aqueoussolution of ammonium persulfate (0.05 mol) and a 20% aqueous solution of2-mercaptoethanol (0.1 mol) were separately and simultaneously droppedinto the reactor in 2 hours. Then, a 20% aqueous solution of ammoniumpersulfate (0.02 mol) was dropped into the reactor in 30 minutes. Theresulting mixture was aged at that temperature (75° C.) for one hour andthereafter heated to 95° C. 35% hydrogen peroxide (0.2 mol) was droppedinto the resulting mixture in 30 minutes and the mixture thus obtainedwas aged at that temperature (95° C.) for 2 hours. Thus, a copolymerhaving a molecular weight of 20,000 was obtained.

Production Example 2 (Admixture C-2)

Water (70 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.1mol of monomer A-2, 0.8 mol of methyl acrylate and 0.1 mol ofmethacrylic acid, a 20% aqueous solution of ammonium persulfate (0.05mol) and a 20% aqueous solution of 2-mercaptoethanol (0.1 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.2 mol) was dropped intothe reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour and thereafter heated to 95° C. 35%Hydrogen peroxide (0.2 mol) was dropped into the resulting mixture in 30minutes and the mixture thus obtained was aged at that temperature (95°C.) for 2 hours. After the completion of the aging, 48% sodium hydroxide(0.07 mol) was added to the mixture. Thus, a copolymer having amolecular weight of 56,000 was obtained.

Production Example 3 (Admixture C-3)

Water (209 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.2mol of monomer A-3, 0.6 mol of ethyl acrylate and 0.2 mol of acrylicacid, a 20% aqueous solution of ammonium persulfate (0.05 mol) and a 20%aqueous solution of 2-mercaptoethanol (0.1 mol) were separately andsimultaneously dropped into the reactor in 2 hours. Then, a 20% aqueoussolution of ammonium persulfate (0.02 mol) was dropped into the reactorin 30 minutes. The resulting mixture was aged at that temperature (75°C.) for one hour and thereafter heated to 95° C. 35% Hydrogen peroxide(0.2 mol) was dropped into the resulting mixture in 30 minutes and themixture thus obtained was aged at that temperature (95° C.) for 2 hours.After the completion of the aging, 48% sodium hydroxide (0.15 mol) wasadded to the mixture. Thus, a copolymer having a molecular weight of134,000 was obtained.

Production Example 4 (Admixture C-4)

Water (58 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.1mol of monomer A-4, 0.7 mol of methyl methacrylate and 0.2 mol ofacrylic acid, a 10% aqueous solution of 2,2'-azobis(2-amidinopropane)dihydrochloride (0.02 mol) and a 20% aqueous solution of2-mercaptoethanol (0.08 mol) were separately and simultaneously droppedinto the reactor in 2 hours. After the completion of the dropping, theresulting mixture was aged at that temperature (75° C.) for one hour andthereafter heated to 95° C. 35% Hydrogen peroxide (0.15 mol) was droppedinto the resulting mixture in 30 minutes and the mixture thus obtainedwas aged at that temperature (95° C.) for 2 hours. After the completionof the aging, 48% sodium hydroxide (0.15 mol) was added to the mixture.Thus, a copolymer having a molecular weight of 68,000 was obtained.

Production Example 5 (Admixture C-5)

Water (101 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.2mol of monomer A-1, 0.6 mol of isobutyl acrylate and 0.2 mol of acrylicacid, a 20% aqueous solution of ammonium persulfate (0.05 mol) and a 20%aqueous solution of 2-mercaptoethanol (0.04 mol) were separately andsimultaneously dropped into the reactor in 2 hours. Then, a 20% aqueoussolution of ammonium persulfate (0.02 mol) was dropped into the reactorin 30 minutes. The resulting mixture was aged at that temperature (75°C.) for one hour and thereafter heated to 95° C. 35% Hydrogen peroxide(0.1 mol) was dropped into the resulting mixture in 30 minutes and themixture thus obtained was aged at that temperature (95° C.) for 2 hours.After the completion of the aging, 48% sodium hydroxide (0.15 mol) wasadded to the mixture. Thus, a copolymer having a molecular weight of112,000 was obtained.

Production Example 6 (Admixture C-6)

Water (56 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.25 mol of monomer A-1, 0.55 mol of ethyl acrylate and 0.2 mol ofmethacrylic acid, a 20% aqueous solution of ammonium persulfate (0.05mol) and a 20% aqueous solution of mercaptosuccinic acid (0.08 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.02 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour. After the completion of the aging,48% sodium hydroxide (0.15 mol) was added to the mixture. Thus, acopolymer having a molecular weight of 86,000 was obtained.

Production Example 7 (Admixture C-7)

Water (56 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.25 mol of monomer A-5, 0.55 mol of methyl acrylate and 0.2 mol ofmonosodium maleate, a 20% aqueous solution of ammonium persulfate (0.05mol) and a 20% aqueous solution of mercaptosuccinic acid (0.08 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.02 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour. After the completion of the aging,48% sodium hydroxide (0.07 mol) was added to the mixture. Thus, acopolymer having a molecular weight of 34,000 was obtained.

Production Example 8 (Admixture C-8)

Water (50 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.25 mol of monomer A-6, 0.55 mol of methyl acrylate and 0.2 mol ofmonosodium maleate, a 20% aqueous solution of ammonium persulfate (0.05mol) and a 20% aqueous solution of mercaptosuccinic acid (0.08 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.02 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour. After the completion of the aging,48% sodium hydroxide (0.07 mol) was added to the mixture. Thus, acopolymer having a molecular weight of 31,000 was obtained.

Production Example 9 (Admixture C-9)

Water (50 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.25 mol of monomer A-7, 0.55 mol of methyl acrylate and 0.2 mol ofmethacrylic acid, a 20% aqueous solution of ammonium persulfate (0.05mol) and a 20% aqueous solution of mercaptosuccinic acid (0.08 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.02 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour. After the completion of the aging,48% sodium hydroxide (0.15 mol) was added to the mixture. Thus, acopolymer having a molecular weight of 53,000 was obtained.

Production Example 10 (Admixture C-10)

Water (30 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.20 mol of monomer A-8, 0.60 mol of ethyl acrylate and 0.2 mol ofmethacrylic acid, a 20% aqueous solution of ammonium persulfate (0.05mol) and a 20% aqueous solution of 2-mercaptoethanol (0.08 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.01 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour and thereafter heated to 95° C. 35%Hydrogen peroxide (0.1 mol) was dropped into the resulting mixture in 30minutes, and the obtained mixture was aged at that temperature (95° C.)for 2 hours. After the completion of the aging, 48% sodium hydroxide(0.15 mol) was added to the mixture. Thus, a copolymer having amolecular weight of 36,000 was obtained.

Production Example 11 (Admixture C-11)

Water (50 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.15 mol of monomer A-9, 0.75 mol of diethyl maleate and 0.1 mol ofmethacrylic acid, a 20% aqueous solution of ammonium persulfate (0.08mol) and a 20% aqueous solution of 2-mercaptoethanol (0.10 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.01 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour and thereafter heated to 95° C. 35%Hydrogen peroxide (0.1 mol) was dropped into the resulting mixture in 30minutes, and the obtained mixture was aged at that temperature (95° C.for 2 hours. After the completion of the aging, 48% sodium hydroxide(0.07 mol) was added to the mixture. Thus, a copolymer having amolecular weight of 54,000 was obtained.

Production Example 12 (Admixture C-12)

Water (50 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.40 mol of monomer A-8 and 0.60 mol of methyl methacrylate, a 20%aqueous solution of ammonium persulfate (0.10 mol) and a 20% aqueoussolution of 2-mercaptoethanol (0.06 mol) were separately andsimultaneously dropped into the reactor in 2 hours. Then, a 20% aqueoussolution of ammonium persulfate (0.01 mol) was dropped into the reactorin 30 minutes. The resulting mixture was aged at that temperature (75°C.) for one hour and thereafter heated to 95° C., 35% Hydrogen peroxide(0.1 mol) was dropped into the resulting mixture in 30 minutes, and theobtained mixture was aged at that temperature (95° C.) for 2 hours.Thus, a copolymer having a molecular weight of 83,000 was obtained.

Production Example 13 (Admixture C-13)

Water (45 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.1mol of monomer A-1, 0.7 mol of methyl acrylate and 0.2 mol ofmethacrylic acid, a 20% aqueous solution of ammonium persulfate (0.05mol) and a 20% aqueous solution of mercaptosuccinic acid (0.08 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.02 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour. After the completion of the aging,48% sodium hydroxide (0.15 mol) was added to the mixture. Thus, acopolymer having a molecular weight of 57,000 was obtained.

Production Example 14 (Admixture C-14)

Water (22 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.2mol of monomer A-8 and 0.8 mol of methacrylic acid, a 20% aqueoussolution of ammonium persulfate (0.02 mol) and a 20% aqueous solution of2-mercaptoethanol (0.05 mol) were separately and simultaneously droppedinto the reactor in 2 hours. Then, a 20% aqueous solution of ammoniumpersulfate (0.01 mol) was dropped into the reactor in 30 minutes. Theresulting mixture was aged at that temperature (75° C.) for one hour andthereafter heated to 95° C. 35% Hydrogen peroxide (0.1 mol) was droppedinto the resulting mixture in 30 minutes, and the obtained mixture wasaged at that temperature (95° C.) for 2 hours. After the completion ofthe aging, 48% sodium hydroxide (0.6 mol) was added to the mixture.Thus, a copolymer having a molecular weight of 23,000 was obtained.

Production Example 15 (Admixture C-15)

Water (70 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.2mol of monomer A-2 and 0.8 mol of methacrylic acid, a 20% aqueoussolution of ammonium persulfate (0.05 mol) and a 20% aqueous solution of2-mercaptoethanol (0.1 mol) were separately and simultaneously droppedinto the reactor in 2 hours. Then, a 20% aqueous solution of ammoniumpersulfate (0.02 mol) was dropped into the reactor in 30 minutes. Theresulting mixture was aged at that temperature (75° C.) for one hour andthereafter heated to 95° C. 35% Hydrogen peroxide (0.2 mol) was droppedinto the resulting mixture in 30 minutes, and the obtained mixture wasaged at that temperature (95° C.) for 2 hours. After the completion ofthe aging, 48% sodium hydroxide (0.6 mol) was added to the mixture.Thus, a copolymer having a molecular weight of 78,000 was obtained.

Production Example 16 (Admixture C-16)

Water (135 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.2mol of monomer A-10, 0.7 mol of methyl acrylate and 0.1 mol ofmethacrylic acid, a 20% aqueous solution of ammonium persulfate (0.03mol) and a 20% aqueous solution of 2-mercaptoethanol (0.05 mol) wereseparately and simultaneously dropped into the reactor in 2 hours. Then,a 20% aqueous solution of ammonium persulfate (0.01 mol) was droppedinto the reactor in 30 minutes. The resulting mixture was aged at thattemperature (75° C.) for one hour and thereafter heated to 95° C. 35%Hydrogen peroxide (0.1 mol) was dropped into the resulting mixture in 30minutes, and the obtained mixture was aged at that temperature (95° C.)for 2 hours. After the completion of the aging, 48% sodium hydroxide(0.07 mol) was added to the mixture. Thus, a copolymer having amolecular weight of 145,000 was obtained.

Production Example 17 (Admixture C-17)

Water (50 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising0.65 mol of monomer A-8 and 0.35 mol of methyl methacrylate, a 20%aqueous solution of ammonium persulfate (0.1 mol) and a 20% aqueoussolution of 2-mercaptoethanol (0.10 mol) were separately andsimultaneously dropped into the reactor in 2 hours. Then, a 20% aqueoussolution of ammonium persulfate (0.01 mol) was dropped into the reactorin 30 minutes. The resulting mixture was aged at that temperature (75°C.) for one hour and thereafter heated to 95° C. 35% Hydrogen peroxide(0.1 mol) was dropped into the resulting mixture in 30 minutes, and theobtained mixture was aged at that temperature (95° C.) for 2 hours.Thus, a copolymer having a molecular weight of 265,000 was obtained.

Production Example 18 (Admixture C-18)

Water (30 mol) was charged into a reactor equipped with a stirrer, andthe resulting system was purged with nitrogen under stirring, followedby heating to 75° C. in a nitrogen atmosphere. A solution comprising 0.2mol of monomer A-11 and 0.8 mol of methyl acrylate, a 20% aqueoussolution of ammonium persulfate (0.1 mol) and a 20% aqueous solution of2-mercaptoethanol (0.06 mol) were separately and simultaneously droppedinto the reactor in 2 hours. Then, a 20% aqueous solution of ammoniumpersulfate (0.01 mol) was dropped into the reactor in 30 minutes. Theresulting mixture was aged at that temperature (75° C.) for one hour andthereafter heated to 95° C. 35% Hydrogen peroxide (0.1 mol) was droppedinto the resulting mixture in 30 minutes, and the obtained mixture wasaged at that temperature (95° C.) for 2 hours. Thus, a copolymer havinga molecular weight of 56,000 was obtained.

Comparative admixtures other than the comparative copolymers were alsoused in the Examples. The comparative admixtures will now be describedtogether with their symbols.

NS

an admixture comprising salt of naphthalenesulfonic acid-formaldehydecondensate (Mighty 150, a product of Kao Corporation), and

MS

an admixture comprising salt of melamine-sulfonic acid-formaldehydecondensate (Mighty 150V-2, a product of Kao Corporation).

Concrete admixtures according to the present invention and comparativeones were evaluated by the following method.

Evaluation as Concrete Admixture

Materials for concrete were prepared according to the conditionsspecified in Table 1.

                  TABLE 1    ______________________________________                  Unit amt. (kg/m.sup.3)    W/C (%)  s/a (%)    C      W      S    G    ______________________________________    57       48         300    170    867  951    ______________________________________     Materials used     W: tap water     C: normal Portland cement, a product of Onoda Cement Co. Ltd. (specific     gravity: 3.16)     S: river sand from the Kino river (specific gravity: 2.60)     G: crushed stone from Takarazuka (specific gravity: 2.63)     s/a: sand/(sand + gravel) (volume ratio)

The materials specified in Table 1 and each admixture were mixed in atilting mixer at 25 rpm for 3 minutes to prepare a concrete. Theconcretes thus prepared were examined for fluidity (slump value)according the method stipulated in JIS-A1101. Then, the concretes wereeach further mixed at 4 rpm to determine the slump value (cm) over theperiod of 120 minutes. The setting time of each concrete was determinedby the method stipulated in JIS-A6204 attachment 1. The initial slump ofeach concrete was adjusted to 20±1 cm by regulating the amount of theadmixture to be added. The results are given in Table 2.

                                      TABLE 2    __________________________________________________________________________                                       Setting time               Amt. of                   Slump value (cm)    (h-min)    Divi-         Symbol of               adding                   just                      after 30                          after 60                              after 90                                  after 120                                       initial                                           final    sion admixture               *.sup.1 (%)                   after                      min.                          min.                              min.                                  min. setting                                           setting    __________________________________________________________________________    Invention         C-1   0.27                   19.0                      21.2                          22.0                              22.5                                  22.5 4-52                                           6-31    product         C-2   0.23                   20.0                      20.3                          20.5                              20.0                                  18.0 4-33                                           6-15         C-3   0.18                   19.5                      20.0                          19.5                              18.0                                  17.5 4-36                                           6-20         C-4   0.18                   20.4                      19.5                          19.0                              18.5                                  17.3 4-39                                           6-28         C-5   0.20                   19.5                      19.5                          18.5                              18.0                                  17.2 4-48                                           6-55         C-6   0.25                   20.8                      20.3                          19.5                              19.2                                  18.5 4-55                                           6-32         C-7   0.29                   20.0                      19.5                          19.0                              18.5                                  15.5 5-13                                           6-58         C-8   0.28                   20.5                      20.0                          19.5                              19.0                                  16.0 5-08                                           6-41         C-9   0.30                   20.5                      20.0                          19.0                              19.0                                  15.5 5-19                                           6-57         C-10  0.26                   19.8                      19.5                          18.2                              17.0                                  15.2 6-02                                           8-13         C-11  0.32                   20.2                      19.9                          19.0                              17.3                                  15.8 5-58                                           7-49         C-12  0.28                   19.2                      19.5                          19.3                              18.8                                  17.6 6-38                                           8-23         C-13  0.25                   20.6                      20.5                          20.0                              19.5                                  19.2 4-52                                           6-27         C-1/C-15*.sup.2               0.22                   20.5                      20.6                          20.5                              20.3                                  20.0 4-18                                           6-02    Comp.         C-14  0.23                   20.7                      18.0                          12.5                              10.5                                  7.0  7-20                                           8-58    product         C-15  0.20                   19.5                      20.0                          19.5                              17.5                                  10.5 4-22                                           6-10         C-16  0.45                   20.0                      16.5                          13.0                              11.0                                  10.0 4-44                                           6-15         C-17  0.38                   19.2                      17.5                          16.3                              12.0                                  8.0  7-06                                           9-26         C-18  0.4 19.5                      16.5                          13.5                              10.0                                  9.5  7-25                                           9-00         NS    0.55                   20.3                      10.5                          8.5 5.0 4.5  7-36                                           9-50         MS    0.60                   20.5                      12.8                          7.0 5.5 4.0  7-48                                           9-36    __________________________________________________________________________     *.sup.1 weight % in terms of solid matter based on the weight of cement     *.sup.2 blend of invention C1 with comparative C15 (weight ratio:     50/50(%))

As apparent from the results given in Table 2, the admixtures of thepresent invention can maintain the slump value observed just after thepreparation for a lengthened time and little retard the hardeningproperty.

Further, the admixtures of the present invention make it possible tomaintain the slump value for two or more hours, while the slump can bemaintained only for at most 90 minutes when the polycarboxylic acidadmixture of the comparative products are used.

Accordingly, a cement composition containing a concrete admixture of thepresent invention shows low level of slump loss for a long time, whichfacilitates the quality control of concrete even in the case whereinconcrete is produced and placed under such conditions that the slump ismore difficult to maintain, for example, high temperature in summer orlow water/cement ratio or even in the case wherein the processing ofconcrete is delayed by some troubles.

C-4, C-5, C-6 and C-13 are in particular preferred.

We claim:
 1. A concrete admixture comprising a copolymer comprising, asstructural units, units derived from an ethylenically unsaturatedmonomer (a) having 25 to 300 moles of C₂ -C₃ oxyalkylene groups per moleof copolymer and units derived from a monomer (b) of an alkyl, alkenylor hydroxyalkyl ester of an ethylenically unsaturated mono- ordi-carboxylic acid.
 2. The admixture as claimed in claim 1, in which thecopolymer further comprises units derived from a monomer (c) selectedfrom the group consisting of an ethylenically unsaturated monocarboxylicacid, a salt thereof, an ethylenically unsaturated dicarboxylic acid, ananhydride thereof and a salt thereof.
 3. The admixture as claimed inclaim 1, in which the copolymer has been obtained by co-polymerising themonomer (a) with the monomer (b) at a reacting ratio of 0.1 to 50 mole %of (a) and 50 to 99.9 mole % of (b).
 4. The admixture as claimed inclaim 2, in which the copolymer has been obtained by co-polymerising themonomer (a), the monomer (b) and the monomer (c) at a reacting ratio of0.1 to 50 mole % of (a), 50 to 90 mole % of (b) and 0.1 to 50 mole % of(c).
 5. The admixture as claimed in claim 1 or 2, in which the monomer(a) is selected from the group consisting of(a-1) an ester productprepared by the reaction between methoxy-polyalkylene glycol having 25to 300 moles of C₂ -C₃ oxyalkylene groups per mole of themethoxy-polyalkylene glycol and either acrylic acid or methacrylic acid,(a-2) a monoallyl ether prepared by the reaction between polyalkyleneglycol having 25 to 300 moles of C₂ -C₃ oxyalkylene groups per mole ofpolyalkylene glycol and allyl alcohol, and (a-3) an adduct prepared bythe reaction between maleic anhydride, itaconic anhydride, citraconicanhydride, maleic acid, itaconic acid, citraconic acid, acrylic amide oran acrylicalkyl amide and a polyalkylene glycol having 25 to 300 molesof C₂ -C₃ oxyalkylene groups per mole of polyalkylene glycol.
 6. Theadmixture as claimed in claim 1 or 2, in which the monomer (a) isdefined by the formula (A): ##STR4## wherein R₁ and R₂ are each hydrogenatom or methyl, AO is a C₂ -C₃ oxyalkylene group, n is a number of 25 to300 and X is hydrogen atom or a C₁ -C₃ alkyl group.
 7. The admixture asclaimed in claim 6, in which n is a number of 110 to
 300. 8. Theadmixture as claimed in claim 1 or 2, in which the monomer (b) is anunsaturated monocarboxylate ester having the formula (B): ##STR5##wherein R₃ is hydrogen atom or methyl and R₄ is a C₁ -C₁₈ alkyl oralkenyl group or a C₂ -C₆ hydroxyalkyl group.
 9. The admixture asclaimed in claim 1 or 2, in which the monomer (b) is selected from thegroup consisting of a maleic diester, a fumaric diester, an itaconicdiester and a citraconic diester, each diester is bonded to a C₁ -C₁₈,straight or branched, alkyl or alkenyl group.
 10. The admixture asclaimed in claim 2, in which the monomer (c) is defined by the formula(C): ##STR6## wherein M₁ is hydrogen atom, an alkali metal, an alkalineearth metal, ammonium, an alkylammonium or a substituted alkylammoniumgroup; R₅, R₆ and R₇ are each hydrogen atom, methyl or (CH₂)_(m2) COOM₂; M₂ has the same definition as M₁ ; m₂ is 0 or
 1. 11. The admixture asclaimed in claim 1 or 2, in which the copolymer has a weight averagemolecular weight of 8,000 to 1,000,000.
 12. The admixture as claimed inclaim 2, wherein the copolymer comprises 10 to 30 mole % of the units(a), 50 to 70 mole % of the units (b) and 10 to 30 mole % of the units(c).
 13. A concrete admixture composition comprising the copolymer asdefined in claim 1 or 2 and at least one high performance water reducingagent selected from the group consisting of naphthalene derivatives,melamine derivatives, aminosulfonic acid derivatives and polycarboxylicacid derivatives.
 14. The composition as claimed in claim 13, in which amixing ratio of the copolymer to the high performance water reducingagent ranges between 10:90 and 90:10.
 15. A method for dispersing acement mixture which comprises adding to a hydraulic composition acopolymer comprising, as structural units, units derived from anethylenically unsaturated monomer (a) having 25 to 300 moles of C₂ -C₃oxyalkylene groups per mole of copolymer and units derived from amonomer (b) of an alkyl, alkenyl or hydroxyalkyl ester of anethylenically unsaturated mono- or di-carboxylic acid.
 16. A method fordispersing a cement mixture according to claim 15, wherein the copolymerfurther comprises units derived from a monomer (c) selected from thegroup consisting of an ethylenically unsaturated monocarboxylic acid, asalt thereof, an ethylenically unsaturated dicarboxylic acid, ananhydride thereof and a salt thereof.
 17. A concrete compositioncomprising cement, aggregates and the copolymer as defined in claim 1 or2.
 18. The concrete composition as claimed in claim 17, which comprises0.02 to 1.0 percent by weight of the copolymer based on solid matter ofthe concrete.